Thermal Limiter Switch

A thermal limiter is much like a fuse. This device was used on many General Motors cars and trucks during the mid to late 1970s and was designed to help protect the compressor inside the air conditioner. The thermal limiter switch keeps the clutch in the air conditioner from engaging when the air conditioning system is low in refrigerant. The superheat switch sends the information to the thermal limiter switch to prevent the clutch from engaging. When refrigerant levels in the air conditioning system are too low, the evaporator within the system will be forced into superheat conditions. This simply means that the vapor from the refrigerant in the system’s evaporator will become overheated. When the superheat switch, which is located in the rear head of the air conditioner’s compressor, gets the signal that the evaporator is being overheated, it will send the message to the thermal limiter switch which will in turn completely shut down the air conditioning system within the vehicle. This is done to prevent damage or failure of the system.

The refrigerant itself plays a vital role in proper maintenance of the air conditioning system in any vehicle. Improper flow of refrigerant can cause damage to the system itself. The refrigerant, when it flows correctly, carries oil to the compressor. The returning refrigerant form the evaporator is cold and helps to provide cooling for the system’s compressor. When the air conditioning system is pushed into superheat mode, the oil and compressor cooling flow is interrupted. The thermal limiter switch helps to prevent this from happening and protects the air conditioner’s compressor from damage due to overheating. A thermal limiter switch is a fixed system. There is typically a capillary tube that helps to monitor the temperature of the air conditioner’s evaporator and helps to cycle to compressor.

The compressor in your vehicle’s air conditioner may fail for two reasons. Typically, they either wear out completely due to many hours of use or an older vehicle that was not properly maintained or they are abused. This abuse happens when the thermal limiter switch does not work properly and the compressor overheats. Of course there are other factors that could contribute to your air conditioning unit suddenly not working properly, but these are the most common reasons why the compressor may stop working properly. This abuse may also happen when you run your car’s air conditioner without properly having the Freon charged. Running it for only a few minutes should not cause any damage. However, if you frequently run the air conditioner or run it for an extended period of time without the proper charge of Freon, you could potentially damage the entire system. Not having your air conditioner properly serviced regularly could also cause the thermal limiter switch to malfunction and could cause damage to the entire air conditioning unit.

Improper servicing of your air conditioning unit could include overcharging the Freon as well as undercharging it as well as installing the wrong replacement starter capacitor, mixing oil types that are not compatible, removing and not replacing or repairing a damaged or improperly working thermal limiter switch and/or having insufficient oil in the system. Installing a new compressor on an air conditioning system that has had problems with acid buildup without properly and thoroughly removing the acid could also cause a problem with the compressor. It is very important to understand the function of the thermal limiter switch and to understand that should you remove this fuse, it needs to be replaced immediately before you begin running the air conditioning system. The thermal limiter was placed in the system to help protect the compressor and removing it without properly repairing it or without purchasing a replacement could cause your entire air conditioning system to be damaged beyond repair.